With several major astronomical surveys beginning to make large-scale cosmological weak lensing measurements in 2013 in order to better understand our cosmological model (including the mysterious dark matter and dark energy), we hope this challenge will prove to have played an important role in identifying promising measurement algorithms and quantifying their performance.

For more information about the challenge, see the menu items above, particularly our links page where you can see how to access the data, submit results, get the software included with the release, and read the challenge handbook.

The server downtime that was mentioned previously is now over, and the GREAT3 leaderboards and data are now available at a new location. All links to the leaderboard on this site and our public GitHub repository should now point to this new location.

The US Mirror for the GREAT3 data will be down for a period of 2-3 days beginning Sunday 30 March 2014. This is while the server at the California Institute of Technology undergoes a significant disk upgrade.

Anyone planning downloads from the US Mirror should avoid those days. We will send a reminder to all participants via the email list closer to the time. The primary download site (based in the UK) will be accessible throughout this period.

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In GREAT3 we have provided a small number of deep fields: longer exposure imaging that overlaps a subset of the main dataset. This sort of deeper imaging is often a part of wide area extragalactic survey strategy. Methods will be able to train using this sort of data in real life, and we wanted to reflect this in GREAT3.

However, those who wish to use the deep fields for the variable PSF or full branches in GREAT3 will find have found that the galaxy catalog files for the deep fields in those branches are missing some important information.

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This morning we recalculated the Q values in all GREAT3 leaderboards following revision of the definition of the metrics, so do not be perturbed if you saw a change in your submission score!

The scaling of the metrics has been revised in light of submission data to ensure that a score of Q~1000 indicates excellent performance, with some allowance for statistical uncertainties. More than one team now appears to be exceeding bias targets in some branches: this is a fantastic achievement.

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We are pleased to announce the release of the ‘variable PSF’ and ‘full’ simulations, which are the last 8 branches of the challenge dataset, as well as updated 'multiepoch’ simulations. As usual, you can download them from the challenge data download page.